Dielectric Constants and Endurance of Chalcogenide Phase-Change Non-Volatile Memory
- PDF / 103,863 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 83 Downloads / 194 Views
0918-H07-06-G08-06
Dielectric Constants and Endurance of Chalcogenide Phase-Change Non-Volatile Memory Semyon D. Savransky1, and Eugenio F. Prokhorov2 1 The TRIZ Experts, 6015 Pepper Tree Court, Newark, CA, 94560 2 CINVESTAV, Unidad Querétaro, Querétaro, 76230, Mexico ABSTRACT Processes in chalcogenide phase-change memory cell are outlined and the importance of a cell’s capacity is noted. Impedances in amorphous Ge-Sb-Te (GST) films are measured and analyzed. Polarization can play a more important role in the formation of native –U centers in Ge2Sb2Te5 than more covalent typical chalcogenide glasses. Reduction of atomic stresses during the –U center’s transformation leads to a high reproducibility of switching cycles (i.e., endurance) in GST and certain other multi-component amorphous chalcogenide alloys suitable for memory and switching devices. INTRODUCTION Optical and electrical memories based on Ge-Sb-Te (GST) films are promising for future generations of information storages such as ultra-high capacity digital versatile disks (DVD) and phase-change non-volatile memories (PC-NVM) [1,2]. Operations in both types of memories are based on fast transitions between amorphous and polycrystalline states that can be numerously repeated under the influence of optical or electrical excitation of the GST alloy. In this paper we try to answer the principal developmental question: “Why is endurance of GST memory pretty good?” We will show that features of intrinsic centers with negative correlation energy (–U centers) allow multiple transitions between high resistivity (RESET) and high conductivity (SET) states of PC-NVM without degradation of the GST alloy properties. We will present experimental results of impedance measurements that support the outlined viewpoint after a short review of the processes which occur during PC-NVM operations. A PC-NVM cell is a simple device with an active material layer between two conductive electrodes [1, 2]. A cell is usually encapsulated in a way that provides a controllable thermal exchange with the environment and is included in a matrix of similar cells connected with regulated sources of electrical signals for cell programming and reading. While reading PCNVM cells is performed by simply sensing the electrical properties of GST in different states, programming includes - Joule heating1 due to positive feedback between GST conductivity and temperature and/or electrical field and/or pressure in the cell, - melting and crystallization of GST in external electrical fields, - threshold switching in high electrical fields [4-10], - vitrification of molten GST (that also occurs in electromagnetic fields for some regimes2). Although the peculiarities of the GST electronic structure can be relevant for all of the mentioned processes in PC-NVM [9, 3], they are vitally important for the threshold switching [59]. Along with this, the displacement current from the parasitic and intrinsic cell capacitors 1 2
The Joule heating of one or both electrodes may also be important. Electromagnetic fields
Data Loading...
